Implantable medical device with antenna

ABSTRACT

An implantable medical device for use in a patient management system is described including a sensor, a processor, and a first communications unit. The first communications unit can deliver notification of significant events to a host computer using a short-range telemetry first communications link. A second communications unit can deliver notification of the significant events to the host computer over a second communications link, which is over a pervasive wireless communications network, such as a cell phone network. The device includes an antenna that is operatively connected to both the first and second communications units.

This application claims the benefit of U.S. Provisional Application No.61/021,202, filed Jan. 15, 2008, the contents of which are hereinincorporated by reference.

TECHNICAL FIELD

This application relates generally to patient management systems, andparticularly, but not by way of limitation, to an implantable medicaldevice having wireless communication capabilities and configured for usein a patient management system.

BACKGROUND OF THE INVENTION

Patient treatment for heart conditions often occurs only after anadverse event such as acutely de-compensated heart failure resulting inhospitalization. However, patients may be provided with an implantedmedical device (IMD) to monitor for signs of impending de-compensationand other problems. IMDs can also provide electrical pacing therapy totreat impending de-compensation and other problems. IMDs can measure andrecord electrical cardiac activity, physical motion and other clinicalparameters.

The data collected by these devices can be retrieved from the device. Ina typical configuration, an IMD is provided with an antenna forcommunicating by telemetry with a device outside of the patient's body.In one case, the device outside of the patient's body is a wand that isheld against or near the patient's body in the vicinity of the implanteddevice. The wand is conventionally magnetically or inductively coupledto the IMD and is wired to a programmer and recorder module thatreceives and analyzes the information from the implanted device and thatmay provide an interface for a person such as a physician to review theinformation. The programmer and recorder module is in turn connected toa host computer which is monitored by medical professionals.

In other cases, an IMD has far-field RF telemetry capabilities, so thatthe IMD can communicate with a monitoring unit in the patient's homewithout requiring any action by the patient. It is not necessary for apatient to place a wand near the implanted device in these systems. TheIMD communicates with a repeater located in the patient's home via a farfield wireless communications link. For example, one known RFcommunication system for these short-range distances is the LATITUDE®Advanced Patient Management system sold by Boston Scientific Corporationof St. Paul, Minn. Such a system usually includes a patient monitordevice that can receive transmissions from an IMD from within about 9 to12 feet. In one known arrangement, a patient places a patient monitordevice in a living space, such as on a stand next to the patient's bed,so that the patient monitor device can receive data transmitted from theIMD while the patient is in proximity to the monitor device. The patientmonitor device is connected to a host computer that is monitored bymedical professionals.

While the use of a patient monitor unit is convenient for a patientwhile located near the repeater, such as within 9 to 12 feet, no datacan be transmitted from the implanted device to the repeater if theimplanted device is out of range. If a medically significant eventoccurs while the implanted device is out of range of the repeater, itwill not be possible to transmit information about the medicallysignificant event back to the host computer at that time.

IMDs provided to heart failure patients frequently are also capable ofelectronic signal processing to deliver a medical therapy. One exampleof a type of implantable medical device is a cardiac rhythm management(CRM) device. CRM devices may include, for example, cardiacresynchronization devices, pacemakers and implantable cardioverterdefibrillators (ICD). These devices generally provide medical treatmentto a patient having a disorder relating to the pacing of the heart, suchas bradycardia or tachycardia. For example, a patient having bradycardiamay be fitted with a pacemaker, where the pacemaker is configured tomonitor the patient's heart rate and to provide an electrical pacingpulse to the cardiac tissue if the heart fails to naturally produce aheart beat at a sufficient rate. By way of further example, a patientmay have an ICD implanted to provide an electrical defibrillation shockto the patient's heart if the patient experiences fibrillation.

IMDs may further be configured to receive instructions from an externalsource to modify and control the operation of the IMD. For example, aphysician may transmit instructions from an external device to animplanted medical device within a patient to change the therapyadministered to the patient in response to the physician's analysis ofinformation received about the patient's condition.

Improved systems for communications of signals to and from implantablemedical devices are needed, especially while the patient is not in rangeof a home monitoring unit.

SUMMARY OF THE INVENTION

In one embodiment, an implantable medical device for use in a patientmanagement system includes a sensor capable of measuring a bodycharacteristic and generating a data signal describing the measurementand a processor configured to analyze the data signal and configured toidentify one or more significant events that warrant attention for thewell-being of a patient. The implantable medical device also includes afirst communications unit including a first wirelesstransmitter/receiver capable of establishing a first communications linkwith a host computer using an external local transmitter/receiver unit,when it is within a short-range telemetry communication range of thelocal transmitter/receiver unit, to deliver at least notification of theone or more significant events to said host computer using said firstcommunications link. The implantable medical device further includes asecond communications unit comprising a second wirelesstransmitter/receiver unit capable of establishing a secondcommunications link with the host computer over a pervasive wirelesscommunications network to deliver at least notification of the one ormore significant events to said host computer over the secondcommunications link. The implantable medical device further includes anantenna operatively connected to both the first and secondcommunications unit.

In another embodiment, a method of telemetry between an implantablemedical device used in a patient management system and a host computerincludes providing an implantable medical device including a sensor andan antenna, and measuring a body characteristic using the sensor andgenerating a data signal that describes the measurement. The methodfurther includes analyzing the data signal and identifying one or moresignificant events that merit attention. Notification of the one or moresignificant events is wirelessly transmitted over the antenna by a firstcommunication unit from the implantable medical device to an externallocal transmitter/receiver unit in the host computer over a firstcommunications link, when the implantable medical device is within ashort-range telemetry communication range of said localtransmitter/receiver unit. When the implantable medical device is out ofrange of the local transmitter/receiver unit, notification of the one ormore significant events from the implantable medical device iswirelessly transmitted over the antenna to the host computer by a secondcommunications unit over a pervasive wireless communications network.

This summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in connection with thefollowing drawings, in which:

FIG. 1 is a schematic representation of an implantable medical device ina patient.

FIG. 2 is a schematic of components of an embodiment of an implantablemedical device.

FIG. 3 is a depiction of a wireless communication network between animplantable medical device and a host computer over a pervasive wirelesscommunication network.

FIG. 4 is a depiction of a communication link between an implantablemedical device and a computing device utilizing a wand.

FIG. 5 depicts a wireless communication transmission from an implantablemedical device when a patient is located near a patient managementdevice.

FIG. 6 depicts an embodiment of a broad-band single mode antenna for usewith the present invention.

FIG. 7 depicts an embodiment of a dual band antenna for use with thepresent invention.

FIG. 8 is an embodiment of a fractal antenna for use with one embodimentof an IMD of the present invention.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, many implantable medical devices are configured totransmit information from the implantable device to a computer or otherdevice located outside of the patient.

Some IMDs are configured to be capable of radio frequency (RF)transmission of data. RF data transmission can require a receiver verynear to the IMD to receive the transmitted signal, or RF datatransmission can communicate over moderate distances, such as within 9to 12 feet. Distances less than 500 feet (152 meters) will be consideredherein to be within a short-range telemetry communication range.

It is desirable to provide communications from an IMD over a greaterdistance than a short-range telemetry communication range. To accomplishthis, a device constructed according to the principles of the presentinvention is configured to communicate with a pervasive wirelesscommunication network. By establishing a communication link with apervasive wireless communication network, longer range communicationsare enabled. Generally, a pervasive wireless communication network is acommunications network that can be used to directly communicate with ahost computer without the need for a repeater device. A pervasivenetwork includes those networks that are sufficiently prevalent ordispersed that an average person in the U.S. would be within range ofinterfacing with the network at some point during a normal dailyroutine. A pervasive wireless network typically has a relatively broadeffective geographic span. There are many different usable pervasivewireless communication networks. One example is a wireless telephonenetwork, such as a cellular telephone network. Other example embodimentsof a pervasive wireless communication network include a wireless pagernetwork, wireless wide area networks (WAN) such as those installed incertain public places like coffee shops, airports, schools, ormunicipalities, and wireless local area networks (LAN) including thosefollowing the standards set forth by the Institute for Electrical andElectronic Engineers (IEEE) in Standards 802.11(b) and (g).

An IMD configured to communicate over a pervasive wireless network maybe further configured to also communicate over a RF transmission linkwithin a short-range telemetry communication range. There may be certainadvantages to communicating over a short-range RF transmissioncommunication link when one is available. For example, a short-range RFtransmission communication is typically more reliable, more secure, andconsumes less power. A short-range RF link is provided for communicatingbetween the IMD and an external local device configured to receiveshort-range RF transmissions, such as the patient monitor devicementioned above.

One of the concerns with enabling communication from an IMD over apervasive wireless communications network, such as a cellular telephonenetwork, is the drain on the battery of the IMD. A typical cell phonechipset consumes a few Watts of power when transmitting. Some commonmedical device batteries such as Li/MnO₂ and Li/SVO batteries candeliver these power levels, but they typically only contain enoughenergy to operate at these power levels for a few hours of cumulativetime, even when not accounting for the power drain of other circuitry inthe IMD. Some common medical device batteries that have been engineeredfor long life, such as Li-(CF)_(x) batteries, are not capable of thesepower levels in the sizes typically used in medical devices.

To address this power concern, one embodiment of an IMD incorporates asecondary rechargeable battery to power the communications over thepervasive wireless network in addition to a primary battery. In thisembodiment, the secondary rechargeable battery supports only thecommunications over the pervasive wireless network, while the primarybattery supports the other components of the IMD, including theshort-range RF communications capabilities. The critical devicefunctionality of the IMD, such as providing therapy to a patient, istherefore not compromised even if the rechargeable battery runs down.Patient compliance concerns are therefore mitigated because only thecommunications capabilities over the pervasive wireless network will becompromised by the patient failing to re-charge their IMD rechargeablebattery.

In addition, an IMD according to the present invention provides at leasttwo separate transmission paths. In one embodiment, a firstcommunications unit with a first transmitter is powered by the primary,non-rechargeable battery and facilitates short-range communication withan external local transceiver that is located within a short-rangetelemetry communication range of the IMD. This first communications unitis used for routine monitoring communications with a host computer, aswell as for emergency communications when necessary. This firstcommunications unit is optimized for low power operation. Wherepossible, hard circuitry is provided to process the data instead ofgeneral purpose processors as will be discussed further herein. The useof hard circuitry results in a less flexible architecture than ifgeneral purpose processors were used for all data handling in the firstcommunications unit. However, the use of hard circuitry where possibleminimizes the power needs of the first communication unit.

A second communications unit with a transmitter/receiver unit is usedfor communications with a pervasive wireless network, such as a cellphone network. The second communications unit includes a transceiver forcommunication with a pervasive wireless network. The secondcommunications unit is only provided with power when it has beendetermined that a communication should occur using the secondcommunication unit. A third communications unit is also provided that iscapable of inductive communications, in some embodiments, as will bediscussed in further detail herein.

In some IMD systems described in past patent publications, a singletransceiver was described as accomplishing both short-range RF telemetrycommunications and communications with a cellular phone network. Whilesuch a system is flexible and may minimize the number of componentswithin the IMD, it has the disadvantage that a relatively power-hungrytransceiver and associated chipset is used for even short-range RFcommunications.

An example embodiment of an implantable medical device 12 implanted in apatient 10 and including a housing 11 is depicted in FIG. 1. In someexamples, the implantable medical device 12 also includes an antenna 13for facilitating wireless communications with a host computer outside ofthe patient's body 10. The implantable medical device according to thepresent invention can be any number of devices including those thatprovide cardiac rhythm management, physiological monitoring, drugdelivery, and/or neuromuscular stimulation. Exemplary implantablecardiac rhythm management devices include pacemakers,cardioverter/defibrillators, and cardiac resynchronization therapydevices. While various aspects of the present invention can be appliedto a number of medical devices, for discussion purposes the medicaldevice 12 is illustrated and described as a cardiac pacemaker. In oneembodiment, the IMD 12 is configured to provide cardiac rhythmmanagement and, as such, is configured with leads 14. Leads 14 contactcardiac tissue at electrode 16. The IMD 12 also includes a sensor 17capable of measuring a body characteristic and generating a data signalthat is representative or descriptive of the measurement taken. In oneexample, IMD 12 includes a sensor 17 that generates a cardiac activitysignal. In another embodiment, the sensor 17 is an impedance sensorcapable of determining a patient's respiration activity. Many othersensors 17 are usable and are known in the art. In some embodiments, IMD12 is a therapy device that determines an appropriate electrical pulsetherapy in response to a condition detected by sensor 17 and deliversthe appropriate electrical pulse therapy to two or more implantedelectrodes 16.

Data from sensor 17 is processed to determine a characteristic of thedata. In some cases, when the data from sensor 17 is processed, it isdetermined that an abnormal or even dangerous situation exists. In oneembodiment, this data signal is analyzed to reveal a medicallysignificant event that merits that the patient receives immediatemedical attention. For example, if the data signal from the IMDindicates the presence of a myocardial infarction or an upcomingde-compensation incident, this situation is identified as a significantmedical event and the patient should seek immediate medical attention.Another medically significant event that is identified in one embodimentis the delivery of a defibrillation shock to the patient. Delivery ofmultiple shocks is a medically significant event in one embodiment.Sometimes the medically significant event merits seeing a physicianwithin 24 hours.

In one embodiment, a processor of the IMD is further configured toidentify a significant device event that threatens correct operation ofthe implantable medical device. Examples of a significant device eventinclude a system fault, a significant change in impedance of implantedleads, and failure of a self-test. A significant change in impedance ofimplanted leads is a change that corresponds to a lead fracture or acrack or breakdown of insulation for a particular configuration of theimplantable medical device.

Further examples of a significant device event include an end of lifebattery state or the device being in a non-therapy mode. Devices aresometimes purposely placed in a non-therapy mode because of thepatient's medical procedures. For example, if a patient with animplanted cardiac re-synchronization device undergoes surgery whereelectrocautery will be used, the device is placed in a non-therapy modeso that the electricity of the electrocautery is not misinterpreted bythe device to be cardiac signals, possibly causing unnecessary therapy.There are other examples of medical procedures that warrant placing anIMD in non-therapy mode. It is possible for an IMD to accidentallyremain in non-therapy mode after the medical procedure. While innon-therapy mode after the medical procedure, the device cannot assist apatient who is experiencing a significant medical event.

Significant medical events and significant device events are twoexamples of significant events that warrant attention to the situationfor the well-being of the patient.

FIG. 2 illustrates one example of an IMD with power management features.The IMD is provided with two separate power sources to provide power tothree separate communication units. In the embodiment of FIG. 2 thefirst communication unit is optimized for low power communicationswithin a short-range telemetry communication range, and a separatesecond communication unit is provided for communication over a pervasivewireless network such as a cell phone network. In addition, a thirdcommunication unit is provided for near-field RF, or inductive,communications. In FIG. 2, solid lines show control and communicationsconnections between the components, while dashed lines indicate powerconnections. A first non-rechargeable power source 20 is provided thatis configured to power a first communication unit 34 and other IMDcomponents, including processor 38, therapy circuitry 32 which includescardiac sensor circuitry 17, an antenna switch 37, data handling logic39, and memory 41.

In one embodiment, the first communication unit 34 is a short-range RFtransmission communication unit and includes a short-range RFtransmitter 35. In some embodiments, the first communication unit alsoincludes a short-range RF receiver 36. In some embodiments, thetransmitter and receiver are combined in a short-range RF transceiver.In some embodiments, the first communication unit 34 is an inductivecommunications unit. In other embodiments, the first communications unituses an acoustic or ultrasonic link to communicate with another device,which is either implanted in the patient's body or in contact with thepatient's skin. The other device may serve as a repeater for thecommunications from the first communications link. Examples ofapparatuses and methods for ultrasonic wireless communication with animplanted medical device are described in U.S. Published PatentApplication 2006/0009818, titled METHOD AND APPARATUS OF ACOUSTICCOMMUNICATION FOR IMPLANTABLE MEDICAL DEVICE, which is herebyincorporated herein in its entirety for any purpose.

In one embodiment, the IMD includes an additional sensor 46 thatmeasures a body characteristic and generates a data signal representingthe body characteristic. The IMD components illustrated in FIG. 2 arenot exhaustive, and the use of many other components is possible.

The first communication unit 34 is specially structured to conservepower during communications to an external local transceiver that iswithin a short-range telemetry communication range. The term short-rangetelemetry communication range refers to 500 feet (152 meters) or less.In some short-range telemetry communication systems, the range is 20feet (6 meters) or less. For inductive transceivers, the telemetry rangeis about 0.5 to 6 inches (1 to 15 centimeters).

The first communication unit 34 receives information from either thesensor 17 or the processor 38 or both. A first wireless transmitter 35of the first communication unit 34 handles the task of transmitting thisdata to an external local receiver or transceiver. In some embodiments,a first wireless receiver 36 receives data from an external localtransmitter, such as confirmation of transmission and programminginformation to alter how the IMD functions. In other embodiments, thefirst communication unit 34 does not have a receiver. In yet otherembodiments, the transmitter and receiver functions are served by acombined transceiver component within the first communications unit 34.

The first communication unit 34 is particularly designed to conservepower. In some embodiments, the first communication unit uses power-onprotocols as described in U.S. Pat. No. 6,985,773, which is herebyincorporated by reference in its entirety. Other examples of powersaving methods and wake-up protocols are described in U.S. PublishedApplication Nos. 2005-0288738, 2005-0027329, and 2005-0240245, which areincorporated herein by reference in their entirety. Wake-up protocolsmay also be sued with respect to the second communication unit.

In addition, the components of the wireless transmitter and receiver areselected to minimize power use. For example, analog components, tailoreddigital components and hard-wired digital components are selected wherepossible in place of more general purpose, more power hungry digitalprocessors. Aspects of the transmission and reception tasks are handledby different components of the first communication unit that can bereferred to as layers.

Physical layer circuitry decodes the data being received and encodes thedata being transmitted, determining if each data bit is a one or a zero.This physical layer circuitry is made of analog circuitry and hard-wireddigital components in one embodiment, rather than utilizing a generalpurpose processor, in order to minimize the power use of the physicallayer. The digital components are tailored to perform a specific logictask, so that they can operate as efficiently as possible for theirpurpose.

The physical layer provides the decoded data to the data link layer whenreceiving, and encodes data from the data link layer when transmitting.The data link layer checks the data for errors and assembles bits intoframes for transmission, or disassembles frames into bits for reception.In one embodiment, the data link layer includes a more versatileprocessor, but also includes digital hard-wired components that handlesome aspects of the data checking. Because the data link layer does notrely exclusively on the function of a processor and because the physicallayer uses some analog components, the power use of thetransmitter/receiver unit is minimized.

Next, the data is provided by the data link layer to the network layer.Here the frames of data are assembled into appropriate packets fortransmission, or packets are disassembled into frames of data uponreception. This function is carried out by a processor. The networklayer also adds addresses of a destination to packets to be transmitted.

Referring again to FIG. 2, second rechargeable power source 40 isprovided that is configured to power a second communications unit 42,where the second communications unit 42 includes a transceiver andchipset 43 that provides for communications over a pervasive wirelesscommunication network. For example, where communication over a cellulartelephone network is desired, a cellular telephone chipset is includedin the second communication unit.

A recharging circuit 44 and recharging transducer 45 are also providedto recharge second rechargeable power source 40. Recharging transducer45 utilizes one of any of a number of known techniques for gettingenergy into a battery in an implantable medical device, such asinductive charging. Inductive charging techniques are taught, forexample, in U.S. Pat. No. 6,553,263, which is hereby incorporated hereinby reference in its entirety for any purpose. Alternatively, therechargeable battery may be recharged by acoustic or ultrasoniccharging. Ultrasonic charging systems for implantable medical devicesare described in U.S. Pat. No. 7,283,874, owned by Boston ScientificCorporation, St. Paul, Minn., and which is hereby incorporated herein byreference in its entirety for any purpose.

In one embodiment, no power is provided to the second communication unit42 unless the processor 38 determines that a communication will be madeover the pervasive wireless network. During a communication over thepervasive wireless network, the second communication unit 42 is poweredon for enough time to negotiate the communication link, up-load therelevant event information, and receive confirmation that it wasreceived. The duration of the use of the second communications unitduring such a communication is likely to be only a 10-60 seconds in manysituations, or 10 to 30 seconds.

In one embodiment, no power is provided to the first communication unit34 unless the processor 38 determines that a communication over the lowpower first communication unit will be made. In one embodiment, no poweris provided to either communication unit until a specific telemetry linkis about to be used.

The first communication unit 34 includes a wireless transmitter and areceiver, in one embodiment, capable of establishing a firstcommunications link from the IMD to an external local transceiver by wayof an RF signal. The external local transceiver is generally in signalcommunication with a host computer, and in some cases the externaltransceiver and the host computer may be housed in the same component.Thereby, when the first communication unit 34 is within a short-range RFtelemetry communication range of the local transceiver, clinical datastored in the IMD may be transmitted to the host computer using thefirst communications link.

An IMD embodiment further includes an inductive communications link.FIG. 2 shows an example embodiment of the components of an IMD having aninductive communication link. The inductive communications link isprovided by way of a third communication unit 80 that includes aninductive transceiver 82 for transmitting and/or receiving inductivecommunications.

An inductive communication link between an IMD and a computer is shownin FIG. 4. As discussed above, an inductive communication link isgenerally accomplished by placing a wand 90 over the patient's chest ina location that is proximate to the implantable medical device 12. Thewand is in signal communication with a computing device 92. This signalcommunication may be wired or may be wireless. An inductive link isestablished between the IMD 12 and the wand 90, and the signal receivedat the wand 90 is then transmitted to the computing device 92.

This communication arrangement has the advantages of high security,because the signal from the IMD is too weak to be detected at more thana very short distance from the IMD. For example, in some embodiments aninductive communication link can be used for authentication andencryption key exchange prior to initiating a RF communication link.U.S. Pat. No. 7,228,182 describes cryptographic systems using aninductive link, and is hereby incorporated by reference in its entiretyfor any purpose. Moreover, there are certain countries where short-rangeRF communication links are not allowed or are limited based on thatcountry's regulation of the electromagnetic spectrum. An inductivecommunication link allows communications to occur in such a situation.

Another benefit of having an inductive communication link capabilityavailable in an IMD is that it allows for another mode of communicationwith the IMD device if the other communication links are not available.For example, if in-band RF interferers are present, the inductivecommunication link could enable communications to occur. An inductivecommunication link also tends to consume relatively little electricalenergy, and as such, can generally be powered from a primary battery,such as first non-rechargeable power source 20.

In one embodiment of an IMD, the IMD does not include short-range RFcommunications, such as RF communications for use with a patient monitordevice placed in the patient's home. Instead, the IMD is configured withan inductive communication link, which is an inductive communicationlink, along with a pervasive wireless communications network link. Inthis arrangement, a patient with an IMD would not need to have ahome-based patient monitoring device, thereby saving the cost of such adevice. Emergency communications could occur over the pervasive wirelesscommunication network as necessary, and routine communications couldeither occur over the pervasive wireless network or over the low-powerRF or inductive communications links based on the availability of each.

A variety of data transmission protocols may be utilized to transmitdata to and from an IMD over a pervasive wireless communication network.For example, General Packet Radio Service (GPRS), may be used, which isa global standard used, for example, by Blackberry devices. It is partof the Global System for Mobile Communications (GSM) standard. This canprovide data rates of about 40 KBPS. Another option is Enhanced Datarates for GSM Evolution (EDGE) or Enhanced GRPS (EGPRS). Date rates ofabout 230 KBPS can be obtained by way of these protocols. Futurecommunication protocols include Wideband Code Division Multiple Access(WCDMA), which may be able to support connections of several MBPS. Interms of operating frequencies, many GSM networks operate in the 900 MHzor 1800 MHz bands, and in the Americas they typically operate in the 850MHz and 1900 MHz bands. Some implantable medical devices presently onthe market have telemetry systems that operate at frequencies near thesebands, such as at 870 MHz or at 914 MHz. It is possible to use the 1800MHz and 1900 MHz band for medical telemetry, although tissue loss wouldbe 4 to 5 dB higher at those frequencies.

In one embodiment, both the first communication unit 34 and the lowpower second communication unit 42 share the same antenna 13. Efficientbio-compatible and bio-conformal antennas take up volume within oraround the IMD, so this feature helps the IMD to minimize overallvolume.

In one embodiment, the antenna is a broad-band, single mode antenna thathas a bandwidth wide enough to cover both the frequency of the secondcommunication unit, such as a cell-phone data connection, and thefrequency of the low-power first communication link, such as an RFtelemetry link. Such an antenna can efficiently cover both the 900 MHzISM band and the 850 MHz GSM band because they are so close infrequency. Exemplary broad-band, single mode antennas are taught incommonly owned U.S. Pat. Nos. 6,456,256, 6,614,406, 6,809,701, which areincorporated herein by reference in their entirety for any purpose.

In one embodiment, a single band antenna is configured to receive andtransmit electromagnetic radiation at frequencies from 800 MHz to 950MHz. In a particular embodiment, the device is configured to receive andtransmit electromagnetic radiation at frequencies from 900 MHz to 950MHz for the short-range radio frequency link, and to receive andtransmit at frequencies from 800 MHz to 900 MHz for the secondcommunication link with the pervasive wireless communication network Anexample embodiment of a broad-band single mode antenna is depicted inFIG. 6. The depicted antenna is a circumferential antenna 100 that issuitable for radiating and receiving far-field electromagneticradiation. The device housing 102 is metallic. One or more therapy leads104 are connected to the circuitry contained within the housing by meansof a header 106. The header 106 is a solid block structure made from asynthetic polymer that has feed-throughs therein for routing electricalconnectors between the therapy leads 104 and the internal circuitry. Theantenna compartment 108 is made of dielectric material and extends fromthe header 106 to wrap circumferentially around a curved portion of thedevice housing 102 with the antenna 100 embedded therein. The antenna100 may be constructed of metal wire such as an alloy made ofapproximately 90% platinum and 10% iridium. Such a material is commonlyused for feed-throughs of therapeutic leads and is both mechanicallystrong and biocompatible. This means that no welding or other means ofattachment is required for attaching the antenna to the device and theantenna can be routed from the transmitting and receiving circuitrywithin the housing through the feed-through to the dielectriccompartment with no interposing connections required. An alternativeantenna and feed-through material is niobium, which has a slightly lowerresistivity than the 90% platinum and 10% iridium alloy. In theembodiment shown in FIG. 6, the wire antenna 100 has a proximal end 100a that exits the device housing through a feed-through and begins itsradiating length around the edge of the device, terminating at thedistal end 100 b.

In a different embodiment, the antenna is a dual-band antenna with tworesonant modes. A dual-band antenna can efficiently cover both the 900MHz ISM band and the 1900 MHz GSM band. Exemplary dual-band antennas aretaught in commonly owned U.S. Pat. No. 7,047,076.

In one embodiment of a dual band antenna, the antenna is configured toreceive and transmit electromagnetic radiation at a first mode havingfrequencies from 800 MHz to 950 MHz and at a second mode havingfrequencies from 1700 MHz to 2000 MHz. In a particular embodiment, theantenna is configured to receive and transmit electromagnetic radiationat frequencies in the first mode from 900 MHz to 950 MHz for theshort-range radio frequency link. The antenna handles the secondcommunication link with the pervasive wireless communication networkeither the first mode at 800 MHz to 900 MHz or the second mode at 1700MHz to 2000 MHz.

An example embodiment of a dual band antenna 110 is depicted in FIG. 7.Antenna 110 is an inverted-f antenna with a transmitting length 112extending along a side 114 of body 1 16. Antenna 110 further includes afeed line 118 that passes through a feed-through 120 where it iselectrically coupled to electronic circuitry within the housing 122. Acutout section 142 is provided to illustrate the connection betweenantenna 110 and housing 122. Further, the antenna 110 includes a shuntarm 124 that extends along a side 126 of the header 128 and that iselectrically coupled to a conductive portion of the header 128 by aconnector leg 130. A side 132 of the header 128 continues beyond theantenna 110.

While the feed-through 120 is shown in FIG. 7 as being in the header128, in other cases, the feed-through 120 can be in an antenna radomeoutside of the header or some other portion of body 116. Further, invarious embodiments the connector leg 130 can be electrically coupled atan electrically conductive portion of the header 128 or the body 116,depending upon the desired attachment location of the antenna 110. Insome cases, the antenna 110 is constructed of one or more materialsincluding, but not limited to, platinum, iridium, stainless steel, orcombinations thereof such as platinum-iridium.

Antenna 110 may include special deployment procedures to limit thepossibility of breaking or deforming the antenna 110. As shown in FIG.7, antenna 110 is disposed within a dielectric housing 134 (alsoreferred to as a dielectric compartment). The dielectric housing 134 canbe formed of a dielectric material coating the antenna 110 in such a waythat the transmitting length 112 is isolated a distance from the housing122, and the antenna 110 is isolated from environmental conditions intowhich the medical device 136 is implanted or deployed. The dielectrichousing 134 can be formed of any type of dielectric material, and wherethe medical device 136 is to be implanted in a human body, choice of thedielectric material may include biocompatibility considerations. Someexamples of dielectric materials include polymers such as parylene,ecothane, tecothane, thermoplastic urethane, polytetrafluooethylene(PTFE), expanded polytetrafluooethylene (ETFE), and/orpolytheretherketone (PEEK).

In embodiments where the medical device 100 is to be implanted in apatient, it may be desirable for medical device 100 to be as small aspossible. This limited size may constrain the carrier frequencies thatcan be used if a quarter-wavelength monopole or half-wavelength dipoleantenna is to be embedded with the device. Further, sharp edges may needto be avoided for patient comfort. Thus, for example, edges 138, 140 ofdielectric housing 134 may be rounded, and/or brought into conformitywith edges of housing 122 such that protrusions are avoided.

An example embodiment of a multimode fractal antenna 300 is depicted inFIG. 8. This fractal antenna is described in detail in U.S. PatentApplication No. 2007-0100385, which is incorporated herein in itsentirety for any purpose.

In a preferred embodiment the fractal antenna is designed with a patternsuch that its intrinsic impedance closely matches the RF circuitry inthe implantable housing. This example minimizes the need for dynamicallyadjustable impedance matching circuitry as part of the implantabledevice, and the resulting device is simpler, more inexpensive and morereliable. In another preferred embodiment the fractal antenna isdesigned to have at least two transmission bands, such as at 400-450 MHzand 862-928 MHz, and not requiring a separate matching circuit foreither band. In another preferred embodiment, the fractal antenna has asingle signal feed point to obtain both of the two preferredtransmission bands.

Fractal antennas typically have multiple resonant paths as a function ofthe repeating nature of the pattern, and thus are broadband radiatorswith multiple efficient transmission bands, while still being verycompact and omni-directional. The small size is a function of thefractal pattern filling in the empty areas of the pattern with smallersized copies of the larger pattern, thus having a space filling propertythat results in long antenna lengths in a small space or volume. Ingeneral, for a given surface area, the length of the antenna that can beplaced in the given surface area improves at an exponential rate foreach iteration of fractal pattern reduction, resulting in better antennaperformance.

FIG. 8 illustrates how four small patterns may be placed to form thelarger pattern 302 of the fractal antenna. This illustration shows how arepeating pattern on different scales may be used to form a fractalpattern, in which a series of different scale views of the pattern eachreveal the same basic underlying structure. Such repeating patterns arehow a fractal antenna may possess many resonance wavelengths.

Referring again to the embodiment of FIG. 2, the first communicationunit 34 has a matching network 47 and the second communication unit 42has a matching network 48. Both matching networks 47, 48 are connectedto the antenna switch 37. The antenna switch 37 switches the antennabetween the two communication units as controlled by the processor 38.The provision of separate matching networks allows optimal matching ofeach of the two communication units 34, 42. It is also possible for thefirst and second communication unit to share a single matching network.In this embodiment, the transmitter/receiver unit and the transceiverare optimized to have similar output impedances. Where differentialoutput is present, the matching networks 47, 48 may include balans fordifferential to single ended conversion.

An example embodiment of a communication network that includes an IMD isdepicted in FIG. 3. In the embodiment of FIG. 3, an IMD 12 is implantedin a patient 10 and is configured to communicate over a pervasivewireless communication network 54. An IMD configured in this wayincludes at least one communication unit that is configured to transmit,and in some cases receive, wireless signals. A pervasive wirelesscommunication network generally includes a network of antennas andtransceivers across a geographic area, such as an antenna 56 configuredto receive signals 58 transmitted from IMD 12. Signals received atantenna 56 are generally transmitted over a network 57 to a remotecomputer 59. Network 57 may comprise any of a number of communicationnetworks, such as wireless or wired communication networks such as theinternet. Remote computer 59 may comprise any of a number of computingdevices, including servers, personal computers, or special purposecomputers. Various additional aspects of the configuration and structureof a pervasive wireless network and communications with an IMD aredisclosed in Published U.S. Patent Application 2004/0122489, which isincorporated herein in its entirety for any purpose.

In the embodiment of FIG. 2, the IMD includes both the capability ofcommunicating over a short-range RF communication link (by way of firstcommunication unit 34) and over a pervasive wireless communication link(by way of second communication unit 42). In one embodiment, theshort-range RF communication link is utilized for any communications,whether routine or emergency in nature, when the short-range RFcommunication link is available, such as when the patient is locatedwithin range of a patient management device. For example, as depicted inFIG. 5, when a patient 10 is within the patient's home and withinsufficient proximity to a patient management device 60, then RF signals61 can be transmitted from the IMD 12 to the patient management device60. The RF signals 61 are received by an antenna 62 of the patientmanagement device 60, which also includes a patient interface 63. Thepatient interface 63 includes display screen 64 for displayinginformation and requesting input from the patient. The patient mayprovide input via patient input devices 66 or a touch sensitive screen.Exemplary patient management devices 60 include, but are not limited to,the LATITUDE® patient management system, the Model 2920 Programmer, andthe Model 3120 Programmer, each available from Boston ScientificCorporation, Natick, Mass. Patient management device 60 is also capableof communicating with a remote computer 68 (also called a remote station70) through telecommunications, such as over a conventional phone line70, through cellular phone communications, or any other wired orwireless form of communication.

Some embodiments of the patient management device 60 do not include apatient interface or display screen. In these embodiments, the patientmanagement device can behave purely as a repeater device, and therebylower cost.

If emergency communications are necessary and the short-range RFcommunication link is not available, such as because the patient is outof range of the patient management device, then the link to thepervasive wireless communication network is used. For example, as seenin FIG. 3, the patient 10 is located away from home and so an emergencytransmission is made from IMD 12 to antenna 56 of a pervasive wirelesscommunication network. In another embodiment, the link to the pervasivewireless communication network is also used for routine monitoringcommunications when the short-range RF link is not available for acertain period of time. For example, if the patient has not been withinrange of the patient management device within 24 hours, then thepervasive wireless communication network will be utilized for routinemonitoring communications. Other time periods are usable.

In an embodiment, an IMD is configured to communicate over the pervasivewireless communication network for emergency communications such as toprovide notification of a significant medical event or a significantdevice event.

The IMD could then utilize the pervasive wireless communication link tomake an emergency communication of this information related to asignificant medical event or a significant device event. The emergencycommunication may be transmitted to a remote computer or medicalfacility, where the content of the communication may be used todetermine a response. In some cases, a remote computer may determinethat the patient's life is at risk and take appropriate actions todispatch medical personnel to treat the patient. In some other cases, amedical worker could receive the information and determine anappropriate response, such as calling the patient or the patient'sphysician. For non-emergency communications, the short-range RF link isgenerally utilized. For example, routine device updates and datadownloads would be conducted over the short-range RF link. However, ifthe IMD has not been within range for establishing the short-range RFlink for a certain defined period of time, such as 48 hours, then in oneembodiment the pervasive wireless communication network link may beutilized.

In one embodiment, the link to the pervasive wireless communicationnetwork is utilized for non-emergency communications so long as thesecond rechargeable power source has at least a certain defined chargelevel. For example, the IMD may be configured to make non-emergencycommunications over the pervasive wireless network so long as the secondrechargeable power source has at least 15 percent of its initial charge.Other percentages are usable, such as if the rechargeable power sourcehas at least 25 percent, 10 percent, or 5 percent of its initial charge.After this charge level is reached, then non-emergency use of thepervasive wireless communication network is avoided and the pervasivewireless communication network link is used only for emergencycommunications.

In a further embodiment, if the rechargeable battery is discharged to apoint where it is not capable of supporting a communication over apervasive wireless network, and there is a need to make an emergencycommunication but the patient is not within range of the short-range RFcommunication link, then the first non-rechargeable battery may be usedto establish a communication link through the pervasive wirelesscommunication network. However, if the state of charge of the firstnon-rechargeable battery is below a certain pre-defined level, such asbelow 5 percent of its initial charge, such that establishing a linkwith the pervasive wireless communication network could causeinsufficient energy to be available to operate the primary functions ofthe IMD for a sufficient period of time, such as the functions thatprovide cardiac pacing and therapy, then the communication is not made,in one embodiment. Other percentages are usable for this threshold, suchas if the primary power source has at least 7 percent, 3 percent, or 1percent of its initial charge.

In one aspect of the operation of an IMD having a pervasive wirelesscommunication network link, it may be possible to determine the locationof the patient when an emergency communication is transmitted. Forexample, if the pervasive wireless communication network link utilizesthe cellular telephone network, it is possible for the cell phone towerequipment to determine the approximate location from which thecommunication signal is being transmitted by determining the angle andorientation of arrival of the signal. Other techniques are known in theart for determining the location of the origin of a cell phonetransmission. By determining the location of the patient, it may bepossible for emergency medical personnel to be dispatched to thepatient's exact location in response to the emergency communication fromthe IMD in order to provide potentially life-saving medical treatment tothe patient. For example, if the IMD determines that the patient isexperiencing or is about to experience a heart attack, the IMD initiatesan emergency communication over the pervasive wireless communicationnetwork, which upon receipt by emergency personnel, is used to determinethe patient's location and to dispatch an ambulance to treat thepatient.

A typical emergency communication over the pervasive wirelesscommunication network would be expected to last about 10 seconds. Thecommunication would only last as long as is necessary to negotiate thecommunication, upload the relevant information, and receive confirmationthat it was received. It is advantageous to make such a communication asshort as possible to minimize the amount of power consumed. However, fora communication that lasts about 10 seconds, it is estimated that ifthis communication was powered by the primary (typicallynon-rechargeable) IMD battery, it would reduce the operative life of theIMD battery by about a few days. This is a generally relatively smallreduction in battery life given the multiple year projected life of thebattery. Furthermore, power consumption may held to a minimum by havingthe pervasive wireless communication network capabilities powered uponly when an emergency communication is being made. The pervasivewireless communication functions are generally not configured to have astand by mode, such as is common in non-implanted devices forcommunicating with a pervasive wireless network, such as a cell phone,thereby further minimizing the power requirements of the device.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise. It should also be notedthat the term “or” is generally employed in its sense including “and/or”unless the content clearly dictates otherwise.

It should also be noted that, as used in this specification and theappended claims, the phrase “configured” describes a system, apparatus,or other structure that is constructed or configured to perform aparticular task or adopt a particular configuration. The phrase“configured” can be used interchangeably with other similar phrases suchas “arranged” “arranged and configured” “constructed and arranged”“constructed” “manufactured and arranged” and the like.

All publications and patent applications in this specification areindicative of the level of ordinary skill in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated by reference.

This application is intended to cover adaptations or variations of thepresent subject matter. It is to be understood that the abovedescription is intended to be illustrative, and not restrictive. Thescope of the present subject matter should be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

1. An implantable medical device for use in a patient management system,said medical device comprising: a sensor capable of measuring a bodycharacteristic and generating a data signal describing the measurement;a processor configured to analyze the data signal and configured toidentify one or more significant events that warrant attention for thewell-being of a patient; a first communications unit comprising a firstwireless transmitter/receiver capable of establishing a firstcommunications link with a host computer using an external localtransmitter/receiver unit, when said first wireless transmitter/receiverunit is within a short-range telemetry communication range of said localtransmitter/receiver unit, to deliver at least notification of the oneor more significant events to said host computer using said firstcommunications link; and a second communications unit comprising asecond wireless transmitter/receiver unit capable of establishing asecond communications link with said host computer over a pervasivewireless communications network to deliver at least notification of theone or more significant events to said host computer over said secondcommunications link an antenna operatively connected to both the firstand second communications unit.
 2. The device of claim 1 wherein theantenna is a dual mode antenna.
 3. The device of claim 2 wherein theantenna is an inverted-f antenna.
 4. The device of claim 1 wherein theantenna is a single mode antenna.
 5. The device of claim 1 wherein thepervasive wireless network is a wireless local area network or wirelesswide area network.
 6. The device of claim 5 wherein the firstcommunication link is a short-range radio frequency link.
 7. The deviceof claim 6 wherein the antenna is a single mode antenna.
 8. The deviceof claim 7 wherein the antenna is configured to receive and transmitelectromagnetic radiation at frequencies from 800 MHz to 950 MHz.
 9. Thedevice of claim 8 wherein the device is configured to: receive andtransmit electromagnetic radiation at frequencies from 900 MHz to 950MHz for the short-range radio frequency link; receive and transmitelectromagnetic radiation at frequencies from 800 MHz to 900 MHz for thesecond communication link with the pervasive wireless communicationnetwork.
 10. The device of claim 6 wherein the antenna is a dual modeantenna.
 11. The device of claim 10 wherein the antenna is configuredto: receive and transmit electromagnetic radiation at a first modehaving frequencies from 800 MHz to 950 MHz; and receive and transmitelectromagnetic radiation at a second mode having frequencies from 1700MHz to 2000 MHz.
 12. The device of claim 11 wherein the antenna isconfigured to: receive and transmit electromagnetic radiation atfrequencies in the first mode from 900 MHz to 950 MHz for theshort-range radio frequency link; receive and transmit electromagneticradiation for the second communication link with the pervasive wirelesscommunication network in one of: the first mode at 800 MHz to 900 MHz,and the second mode at 1700 MHz to 2000 MHz.
 13. The device of claim 1further comprising: a first matching network operatively connected tothe first communications unit and the antenna; and a second matchingnetwork operatively connected to the second communications unit and theantenna.
 14. The device of claim 1 wherein the antenna is a fractalantenna.
 15. The device of claim 1 wherein the one or more significantevents comprise one or more significant medical events that meritmedical attention including any of a myocardial infarction, cardiacsignals indicating an upcoming de-compensation incident, and delivery ofa defibrillation shock by the implantable medical device.
 16. The deviceof claim 1 wherein the one or more significant events comprise one ormore significant device events that threaten correct operation of theimplantable medical device including any of a system fault, asignificant change in impedance of implanted leads, an end-of-lifebattery state, a reset of the device, the device being in non-therapymode, and failure of a self-test.
 17. A method of telemetry between animplantable medical device used in a patient management system and ahost computer, comprising: providing an implantable medical devicecomprising a sensor and an antenna; measuring a body characteristicusing the sensor and generating a data signal that describes themeasurement; analyzing the data signal and identifying one or moresignificant events that merit attention; wirelessly transmitting overthe antenna by a first communication unit from the implantable medicaldevice to an external local transmitter/receiver unit in the hostcomputer over a first communications link, when said implantable medicaldevice is within a short-range telemetry communication range of saidlocal transmitter/receiver unit, to deliver at least notification of theone or more significant events to said host computer using said firstcommunications link; and when said implantable medical device is out ofrange of the local transmitter/receiver unit, wirelessly transmittingover the antenna notification of the one or more significant events fromthe implantable medical device to the host computer by a secondcommunications unit over a pervasive wireless communications network.18. The method of claim 17 wherein wirelessly transmitting over thepervasive wireless network comprises transmitting over a wireless localarea network or wireless wide area network.
 19. The method of claim 18wherein wirelessly transmitting over the first communication linkcomprises transmitting over a short-range radio frequency link.
 20. Themethod of claim 19 wherein wirelessly transmitting over the firstcommunication link comprises transmitting at frequencies from 900 MHz to950 MHz; and wirelessly transmitting over the second communication linkcomprises transmitting at frequencies from 800 to 900 MHz.
 21. Themethod of claim 17 comprising: receiving and transmittingelectromagnetic radiation at a first mode having frequencies from 800MHz to 950 MHz; and receiving and transmitting electromagnetic radiationat a second mode having frequencies from 1700 MHz to 2000 MHz.
 22. Themethod of claim 21 comprising: receiving and transmittingelectromagnetic radiation at frequencies in the first mode from 900 MHzto 950 MHz for the short-range radio frequency link; receiving andtransmitting electromagnetic radiation for the second communication linkwith the pervasive wireless communication network in one of: the firstmode at 800 MHz to 900 MHz, and the second mode at 1700 MHz to 2000 MHz.